We liked the Fitbit One activity tracker, but there was some convenience lacking. While its pebble-like form-factor was very discreet, it meant you always had to take it out and put it in a special arm band if you wanted to monitor your sleep, then return it to your pants in the morning. And which pants did you forget them in this time?

Last month we reviewed the Fitbit Zip, which was basically a glorified pedometer. The Fitbit One is …
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Fitbit apparently heard our impatient grumblings and has released their first activity and sleep tracking wristband, the Fitbit Flex.

The Flex looks more like the Jawbone Up than other Fitbit products. It's the company's first tracker without a built-in screen. Instead it has five LEDs that like up one by one as you move toward your goal (10,000 steps in a day, for instance) in 20 percent increments. It makes up for the lack of a display, though, by being among the first activity trackers to use Bluetooth 4.0 to sync with newer iOS and Android devices. The Flex will push data to Fitbit's rather robust mobile app, giving you data about steps taken, calories burned, and other metrics. It also comes with a USB dongle for wirelessly syncing with your computer.

Jawbone has given its life-tracking Up bracelet a second chance. The original was promising, but…
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Like the Fitbit One, the Flex is designed to track the duration and quality of your sleep (i.e. how many times you stirred or woke). It also has that vibrating silent alarm feature we liked so much, and which your partner will probably appreciate. But aside from the screen, there is one more feature found in the One that didn't make it into the Flex: an altimeter. One of the best things about the One is that it didn't just count your steps, but how much elevation you gained, which gives you a much more accurate picture of how active you've been and how many calories you've burn. It's a shame that was left out.

The Flex will come in five colors: Black, Slate, Teal, Tangerine, Navy. The tracker itself detaches, so you purchase multiple bands if you want. At last, a fitness track to match your tangerine pants. You can pre-order today for $100 and they will begin shipping sometime in the spring. [Fitbit]